1. Field of the Invention
The present invention relates to a contact probe able to reduce contact resistance between the plunger and the barrel and to enhance durableness.
2. Related Prior Art
Electrical inspection of discrete semiconductor device such as laser diode and wafer forming a plurality of devices therein uses a contact probe. Specifically, for the inspection of a semiconductor device, a tip of the plunger elastically comes in contact on a pad of the device to measure the electrical performance and to supply the power to the device.
Typical contact probe provides a plunger, a barrel to receive the plunger and a spring to push the tip of the plunger out of the barrel. The plunger and the barrel may be made of electrically conductive material. The plunger may slide along the axis of the barrel and the electrical conductive path may be formed by making the plunger in contact to the inner surface of the barrel.
A Japanese patent application published as JP 2002-202323A has disclosed a contact probe that provides a mechanism to convert rectilinear motion of a pin into rotational motion around an axis. Another Japanese patent application published as JP2006-090941A has disclosed a contact probe with a plunger, a bias pin and a spring, in which the plunger has a sloped surface in a side facing the spring, while, the bias pin has a tapered surface in a side facing the plunger, and the bias pin is arranged between the plunger and the spring. A Japanese patent Application published as JP2004-069508A has disclosed another contact probe with a plunger whose tip has a crown shape.
A conventional contact probe has a plunger with a limited area coming in contact with the barrel. The plunger, by sliding along the axis of the barrel, a limited surface of the plunger always comes in contact with the barrel. Accordingly, an iterating use of the probe causes abrasion the area, which makes the contact resistance therebetween instable and the durability the durability worse. The crowned shape of the tip of the plunger disclosed in the Japanese patent mentioned above may rotate itself and vary the area to come in contact with the conductive tube by butting against the solder ball. However, the rotation of the plunger strongly depends on a condition of the crowned tip of the plunger and the area coming in contact with this tip. Accordingly, a flat area may not induce the rotation of the plunger and prevent the abrasion of the area securely.